On the day of October 21st, 2013, the world changed. At exactly 4pm, every human gained a gift. The living thing they touched, they merged with. If it was another human, the merger would add the strengths of both and merge the personalities. If the person was of the opposite sex, the result was a fertile hermaphrodite. If they were to touch an animal (must be an animal, and large enough to be seen and purposely touched) they become an anthro-version of said animal (always human shaped), and gain the instincts and slight benefits of that animal. If the animal was of the opposite sex to the person, the result is the animals gender. If the animal went into heat for mating, so would the anthro result, with the pheromones working on full humans and the said anthro species. Size changes only work up to a foot in difference from their normal height. Fertility with anthros only carries with another anthro of the same species or a human (hermaphrodite or otherwise), in which case the child is an anthro. Every person in the world merges with something/one by the end of the day, and people just accept that this is how the world is from now on, aside from minor personal freakouts. When changing gender, the result is bi.
Let's start by choosing a protagonist.